Generally, in a hydraulic system that is applied to a construction machine, such as an excavator, a plurality of hydraulic pumps are connected to an engine. A left traveling device (TL) and a working device, such as a boom or a bucket, are connected to one of the hydraulic pumps, and a right traveling device (TR), a working device, such as an arm, an option device, and a swing device are connected to the other of the hydraulic pumps.
When a combined operation for simultaneously operating a working device, such as an arm, and a swing device (e.g., excavating earth and sand, performing a swing operation, and loading a dump truck or the like with excavated earth and sand) is performed, a part of a flow rate, which is supplied to a working device side by a priority valve, is limited to secure operability of the swing device that has a relatively large load. Through this, during the combined operation of the arm and the swing device having different loads, the load of the swing device side is increased to secure complex operability.
A flow control valve for a construction machine in the related art, as illustrated in FIG. 1, includes a valve block 3 in which a pump path 4 connected to a hydraulic pump (not illustrated) and connection ports 1 and 2 communicating with a hydraulic actuator (e.g., arm cylinder) are formed; a spool 5 slidably installed inside the valve block 3 and shifted in a left or right direction according to any one of pilot signal pressures Pi1 and Pi2 applied thereto to control hydraulic fluid that is supplied from the pump path 4 connected to the swing device side to the connection ports 1 and 2; and a priority valve 8 mounted on the valve block 3 to limit a flow rate that is supplied from the pump path 4 to a path 7 communicating with the connection port 2 if a control spool 6 is shifted according to pilot signal pressure Pi3 of the swing device side that is simultaneously applied during a combined work for simultaneously operating the working device, such as an arm, and the swing device.
If any one of the pilot signal pressures Pi1 and Pi2 is applied to the valve block 3, the spool 5 is shifted in the left or right direction as shown in the drawing, and thus the hydraulic fluid that is discharged from the hydraulic pump (not illustrated) is supplied to the connection ports 1 and 2 communicating with the actuator (arm cylinder) through the pump path 4, the path 7, and a parallel path 9 in order.
In this case, if the pilot signal pressure Pi3 of the swing device side is simultaneously applied to the priority valve 8 during the combined operation for simultaneously operating the working device, such as the arm, and the swing device, the control spool 6 is shifted (i.e., the pilot signal pressure Pi3 exceeds an elastic force of a valve spring 12) in the right direction as shown in the drawing to lower the flow rate that is supplied from the pump path 4 to the path 7. Accordingly, the hydraulic fluid pressure on the side of the pump path 4 is increased, and thus the hydraulic fluid pressure of the swing device side that communicates with the pump path 4 is increased to secure the complex operability.